The present invention relates to a device for controlling distance for a motor vehicle, the device observing a setpoint distance or a setpoint time gap with respect to a vehicle driving ahead as a function of the traveling speed, and the distance control taking a minimum distance or a minimum time gap, specifiable by the driver, into consideration when determining the setpoint distance or the setpoint time gap.
A distance control for motor vehicles is described in German Patent No. 44 37 678. It describes the distance control system known as an ACC system (adaptive cruise control system). In that case, the distance and/or the relative speed with respect to the motor vehicle driving ahead is usually determined by a measuring device operating according to the radar or laser principle. With this information about the distance or the relative speed, the speed of one""s own vehicle is controlled by an intervention in the drive and/or the brake of the vehicle in such a way that the distance to the vehicle driving ahead corresponds to a predefined setpoint distance. Instead of the setpoint distance, the variable equivalent thereto, namely, a setpoint time gap between the two vehicles following one another, can also be regulated.
Usually, the setpoint distance corresponds to a defined speed-dependent safety distance. However, a fixedly defined safety distance or a definitively predefined setpoint time gap is often not compatible with the personal driving style of a driver. Thus, sporty drivers will more likely prefer a smaller distance to the vehicle driving ahead, while a driver having a steadier driving style will want to follow a preceding vehicle at a greater safety distance. In order to take the driver""s wish into account, according to German Patent No. 44 37 678, the possibility is given to the driver to set a minimum distance or a minimum time gap desired by him/her via an operating control element. This stipulation by the driver is taken into account during the determination of the setpoint distance or the setpoint time gap by the adaptive cruise control system. According to the related art, when ascertaining the setpoint distance or the setpoint time gap in view of the drivers wish, no differentiation is made as to whether visibility is good or poor.
Given poor visibility, i.e. during bad weather and/or when it is dark, the driver perceives a given distance to a preceding vehicle to be shorter than in the case of normal visibility as prevails during the day and under good weather conditions. Therefore, an object of the present invention is to take the different distance impression of the driver, depending upon whether good or poor visibility prevails, into account when the setpoint distance or the setpoint time gap is determined by the distance control.
The indicated objective is achieved in that, in response to poor visibility, the distance control increases the setpoint distance or the setpoint time gap ascertained for normal visibility. Namely, the driver then no longer perceives the setpoint distance (setpoint time gap) set by the distance control, taking into account the driver""s wish, to be smaller compared to the setpoint distance (setpoint time gap) during good visibility.
Accordingly, to recognize poor visibility, sensors are provided which detect indications of bad weather and/or darkness. Among these are preferably sensors which, for example, detect the visual range, the road condition, the windshield wiper activity, the switching on of fog lights, precipitation (rain, snow, fog), the brightness of the surroundings, the switching on of headlights.
Preferably, the distance control increases the setpoint time gap during poor visibility by 20 to 30% compared to normal visibility.